利用电子散斑相移技术测量物体三维面形的方法

为了获得准确的面形测量,提出了一种相移电子散斑干涉技术测量物体面形的测量方法.利用电子散斑干涉产生载波条纹,该载波条纹受到物体表面高度的调制变得弯曲,引起载波条纹相位的变化,可运用相移技术提取物体的相位信息,最后根据高度和相位之间的关系得到物体的面形.介绍了该方法的原理,利用该方法对球冠物体进行了面形测量,证明该方法测量物体面形是可行性的.由于是采用散斑干涉的方法产生干涉条纹,因此该方法测量物体面形具有灵敏度高的优点.     

利用电子散斑相移技术测量物体三维面形的方法

为了获得准确的面形测量,提出了一种相移电子散斑干涉技术测量物体面形的测量方法.利用电子散斑干涉产生载波条纹,该载波条纹受到物体表面高度的调制变得弯曲,引起载波条纹相位的变化,可运用相移技术提取物体的相位信息,最后根据高度和相位之间的关系得到物体的面形.介绍了该方法的原理,利用该方法对球冠物体进行了面形测量,证明该方法测量物体面形是可行性的.由于是采用散斑干涉的方法产生干涉条纹,因此该方法测量物体面形具有灵敏度高的优点.     

测量物体位移的数字白光散斑照相术

给出了一测量物体刚体位移的数字白光散斑照相术。数字傅里叶变换从双曝光字白光散斑图用来产生杨氏条纹。该杨氏条纹能够用数字傅里叶变换结合条纹重构进行自动分析。此外，给出一种条纹质量增强的方法。     

载频调制大剪切电子散斑干涉系统

大剪切电子散斑干涉技术不需要引入参考光，具有条纹质量好等特点。提出将干涉场的载频调制技术引入到大剪切电子散斑干涉中，可形成具有载频调制功能的新的电子散斑干涉系统。该系统具有对测量环境的隔振振动要求低，能方便定量求解物体的变形场等优点。首先讨论大剪切载频的调制机理，然后利用中心加载、周边固定的圆盘进行典型实验，设计了可用计算机控制且可对参考物进行精确偏转的步进电机系统，进而实现了对电子散斑干涉场的自动控制调制。最后，利用傅里叶变换法对调制条纹进行解调，解调出变形场的相位，并通过相位与位移的转换计算，得到精确的物体变形场。实验结果证明，该系统能够调制电子散斑干涉场，求解物体的位移场。     

利用散斑嵌入条纹和查找表进行三维面形测量

为了快速、准确地重建复杂场景的三维面形,提出了一种利用散斑嵌入相移条纹图案和截断相位-高度查找表的三维面形测量方法。将散斑作为辅助信号嵌入到四步相移条纹图案的相位分布中,得到待投影的复合条纹图案。利用相移算法解调出被测物体的截断相位和额外的散斑信息。利用查找表得到截断相位对应的多个候选高度,再利用散斑对条纹周期进行标记以解决高度歧义问题,唯一确定截断相位所对应的正确高度,以实现被测物体三维面形的快速重建。该方法直接从截断相位信息中重建三维面形,无需投影任何附加图案,也无需进行相位展开。理论分析和实验结果表明,该方法可以实现动、静态复杂场景三维形貌的高精度测量且鲁棒性好。     

基于条纹等值线相关的散斑条纹图处理新方法

在数字散斑干涉术中,通常由物体变形前后得到的两幅原始散斑场用相减方法来得到条纹图,并由相移后的多幅(三幅以上)条纹图来求取相位场。介绍了一种基于条纹等值线相关的条纹图生成新方法,并在此基础上提出了基于单幅干涉条纹图的相位场提取新方法和基于条纹等值线相关的单步相移新方法。实验结果表明,该方法具有良好的结果和发展前景。     

基于电子散斑干涉与数字剪切散斑干涉法的悬臂薄板振动分析

基于激光光路的光波随机相位扰动,分析了电子散斑干涉实时图像相减时模态条纹图的形成机理,提出了一种振幅涨落测量法。搭建了用于离面振动分析的电子散斑干涉和数字剪切散斑干涉测量系统,并对完整和含狭缝的悬臂铝板的振动特性进行了实验研究。实验结果表明,实时图像相减模式获得的模态条纹图对比度明显优于其他方法,得到的前10阶模态条纹图与有限元法计算结果具有良好的一致性。相比于电子散斑干涉法,数字剪切散斑干涉法对试样局部的刚度变化和缺陷更敏感。     

一种利用散斑干涉和灰度等级测量纳米级位移的新方法

为了解决散斑干涉计量中亚波长位移测量的困难，相移技术被广泛使用，但相移技术有其固有缺点，应用非常麻烦。这里提出一种不同于已往相移技术的全新微小位移测量方法。即把灰度等级法和散斑干涉计量相结合以实现对亚波长位移或变形的测量。克服了散斑干涉计量中变形或位移小于半个波长不产生完整条纹时计量困难的缺点,论述了其测量原理并进行了实验。实验结果很好地证明了上述方法的可行性。为精密散斑干涉计量提供了一种更简单有效的方法。     

平行式向列液晶实现相移剪切电子散斑干涉术的研究

研究了向列型液晶的相位调制特性，采用平行式向列液昌作为相移器建立了相移剪切电子散斑干涉计量系统。该方法将相移技术引入到剪切电子散斑干涉术中，提高了检测精度，采用了相关条纹法求解相位，简化了计算；相移方法简单，可靠。用该系统进行应变场的测量实验，取得了满意的效果。     

孔径旋转频闪散斑照相法测量物体的固有频率

提出了一种测量物体固有频率的新方法－－孔径旋转频闪散斑照相法。该方法能方便地测量振动物体的固有频率，具有精度高、全场显示、条纹可见度好等优点，给出了理论分析和实验结果。     

Vibration Analysis by Phase Shifting Digital Holography

Phase-shifting digital holography has been used for the study of vibrating objects. The time-averaged complex amplitude of Fresnel diffracted field due to a vibrating object was obtained by using a three-step phase-shifting algorithm. Taking the inverse Fresnel transform of the complex amplitude resulted in an image of the object superimposed with Bessel fringes. The Bessel fringes are contour map of the vibration amplitude. By sinusoidally modulating the phase of the reference beam at the vibration frequency, the brightest fringe could be shifted to points of interest, thus extending the measurable range of vibration amplitude.     

A comparative study of phase-shifting algorithms in digital speckle pattern interferometry

Digital speckle pattern interferometry (DSPI) is a tool for making qualitative as well as quantitative measurements of deformation of objects. Phase-shifting algorithms in DSPI are useful for extracting quantitative deformation data from the system. Comparative studies of the different phase-shifting algorithms in DSPI for object deformation measurement are presented. Static and quasi-dynamic deformation of the object can be measured using these algorithms. Error compensating five-step phase-shifting method is used for the algorithms.     

Measuring velocity of speckle fields with digital speckle pattern interferometry

We investigate a digital method for detecting the velocity of a diffusing object. The technique is based on Digital Speckle Pattern Interferometry (DSPI). A set of reference fringes is generated externally through the reference beam in a digital interferometer. As the object moves, subsequent frames are acquired and subtracted according to the normal DSPI procedure and stored. By means of the theory of first order speckle statistics applied to speckle intensity correlation, we relate the visibility variations in the reference fringes with the object velocity. Thus, by measuring the fringe visibility variation in the resulting DSPI stored frames the mean object velocity can be obtained. The theoretical results are experimentally verified.     

A composite-structured-light 3D measurement method based on fringe parameter calibration

This paper proposes a novel method for reducing measurement error caused by spectrum overlapping in composite-structured-light 3D measurement systems. For a composite-structured-light 3D measurement system, spectrum overlapping causes parameters of each deformed phase-shifting fringe to change, and therefore leads to phase measurement errors. The proposed fringe parameter calibration method is based on the fact that variations in each deformed fringe's parameters are independent of height and reflectivity of the measured object. Three frames of composite grating are projected on the reference plane, and each carrier channel includes the information of three phase-shifting sinusoidal gratings used in Phase Measuring Profilometry (PMP). With the parameter calculation formulas of PMP, the parameters of fringes demodulated from the same carrier channel can be calculated, and therefore parameter relation coefficients between fringes demodulated from different carrier channels may be obtained. When an object is measured, these relation coefficients can be used to calibrate the parameters of the deformed phase-shifting fringes. A new 3D measurement mathematical model is established to reconstruct the shape of the object. Experimental data proved that the proposed method can effectively restrain the effect of spectrum overlapping and improve measurement accuracy by more than three times.     

Shifted-phase calibration for a 3-D shape measurement system based on orthogonal composite grating projection

This paper proposes a novel method for reducing measurement error caused by spectrum overlapping in orthogonal-composite-grating-based 3-D measurement method. For 3-D measurement systems based on orthogonal composite grating projection, spectrum overlapping causes phase of each deformed phase-shifting fringe changed differently, which violates the principle that the shifted phases between adjacent deformed fringes must be equivalent to 2π/3, and therefore results in phase measurement error. The proposed shifted-phase calibration method is based on that phase variation of each deformed fringe is independent of height and reflectivity of the measured object. Three composite gratings are projected on the reference plane, and each carrier channel includes three phase-shifting gratings needed in phase measuring profilometry (PMP). Because the adjacent phase-shifting fringes demodulated from the same carrier channel have the phase difference of 2π/3, we can respectively calculate the reference plane's phases of three carrier channels by the phase algorithm of PMP method, and the shifted phases between them are obtained. When an object is measured, the shifted phases between deformed phase-shifting fringes can be calibrated. A new 3-D measurement mathematical model is set to reconstruct object. Our experiments prove that the proposed method can effectively restrain the effect of spectrum overlapping and improve measurement accuracy almost one times.     

通过相移条纹图差分测定相移量的方法

提出一种通过两幅相移条纹图相减来确定它们之间相移量的方法,进行了理论分析和实验验证。两幅相移条纹图相减并归一化后,得到的相移差分函数是振幅只与相移量有关的正弦函数,可以通过确定该函数最大极值的方法得到振幅,进而计算出相移量。介绍了极值直接查找法和平均法两种实现最大极值测量的方法。由于不使用傅里叶变换,减少了运算时间,既可以用于高空间频率条纹,也可以用于稀疏平行条纹,以及任意花样的条纹。在衬比度因子确定后,用这种方法就能够直接在空域内确定两幅条纹图之间的相移量,通过大量采样点进行统计计算,使结果达到很高的精度。将所得到的结果与用傅里叶变换方法得到的结果进行了比较,表明两种方法得到的结果具有完全相同的精度。     

A flexible 3D profilometry based on fringe contrast analysis

This paper proposed a flexible 3D profilometry based on fringe contrast analysis. A series of sinusoidal fringes are projected on the surface of the testing object that is laid in front of the imaging plane of the fringes, and captured through a beam splitter by a CCD camera in the same direction as the axis of the projection. After the fringe contrast obtained using phase-shifting technique, the height of the object can be restored through searching the look-up table of the contrast and the height. In the measurement process, we only need to capture fringe patterns in one position, without changing the imaging plane of the fringes, so it is faster and more convenient than the existing method based on fringe contrast analysis. Our system is simple and flexible by reason of no special devices used. In this paper, the principle of this method, the setup of the measurement system and primary experiment results are given. The experimental results prove this method can restore the height of the complex object accurately and effectively.     

Vibration analysis and non-destructive testing with real-time shearography

Real-time laser speckle shearography coupled with vibration stressing is shown to be an effective means of vibration analysis and non-destructive testing. The shearograms are modulated by a system of live fringes. These fringes are shown to be described by the zeroth-order Bessel function of the first kind and their visibility decreases with increasing fringe order. In vibration analysis, the instantaneous fringe pattern depicts the out-of-plane surface displacement gradient of the object surface at various resonance modes. In non-destructive testing, the flaw depth in a component can be determined without having to determine fringe orders. There is good agreement between the results obtained using the method and those from theory and time-average holography. A major advantage of real-time shearography is its facility for continuous assessment of a vibrating object without the need for secondary shearogram reconstruction.     

Measurement of static and vibrating microsystems using microscopicTV holography

This paper describes a microscopic TV holographic arrangement to study the static and vibrating microsystems. In the optical setup, the object beam and the reference beam arms are provided with a phase shifting mirror and a bias phase modulation mirror to carry out the measurement of the out-of-plane deformation and the vibration amplitude fields, respectively. A long working distance microscope is used in the setup for magnifying and imaging the objects on to the CCD camera. For static fringe analysis, the system is used in double exposure subtraction mode of operation, while for vibration fringe analysis, it is used in the time average contrast reversal refreshing mode of operation. An improved approach for qualitative analysis of time averaged fringes helps in reducing the number of frames required for analysis. The usefulness of the system is demonstrated by examples of static and vibration measurements for different microobjects.     

Accurate measurement of composite laminates deflection using digital speckle pattern interferometry

The modern digital speckle pattern interferometry (DSPI) technique is applied for the accurate measurement of the full-field deflection distribution of a bent composite laminates. Two kinds of powerful phase-shifting methods, phase of differences method (PDM) and difference of phases method (DPM), are described briefly and employed in DSPI to quantitatively extract the phase information, respectively. A comparison of the deflection distributions measured by DPM and PDM indicates that the former has a better measurement accuracy than the latter in laminate's static test experiment.